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Development of a New Efficient and Accurate Available Bandwidth
Estimation Method
Péter Hága
Attila Pásztor
István Csabai
Darryl Veitch
Viktória Hunyadi
CNL - Network Performance Measurement Group2
Outline
• Available bandwidth measurements, motivations• Definition of Available Bandwidth • Milestones in the evolution of AB measurement• Measurement Method, and results from simulation• Analytic Approximation• Estimation of AB• Laboratory Experiments • Conclusion and Future Plans
CNL - Network Performance Measurement Group3
Importance of available bandwidth measurements,motivations
The knowledge of available bandwidth along a route is important:• for call admission control• congestion control and avoidance• determine the instantaneous free transmission capacity
The motivations behind developing methods to estimate AB:• applications cloud use it to adopt their behaviour• avoid congested paths • determine the optimal transfer rate without losing packets
CNL - Network Performance Measurement Group4
Definition of Available Bandwidth
Available bandwidth of hop h, over the time interval T,T(roughly the difference of the link capacity and the average cross traffic)
Available bandwidth of a route is a smallest hop AB on a path:
CNL - Network Performance Measurement Group5
Milestones in the evolution of AB measurements problems, advantages
Pathload: binary search algorithm• invasiveness - high rate probing results burst of packet trains• time - iteration requests significant amount of time • non-stationary of cross traffic - binary search can results contradictory results
PathChirp: chirp based measurement• estimation from measured data is heuristic • fine timescale
New class of probing techniques: interaction class (between probes and CT)• not requiring a knowledge of the link bandwidths• not requiring a knowledge which link is a narrow link
CNL - Network Performance Measurement Group6
Our goal
improve a method to estimate AB, which:• based on theoretical model• can give us accurate estimations• with high frequency• develop a tool to make our accurate estimations in robust way• make this tool widely accessible for use it in smart applications (eg. transfer protocols)
CNL - Network Performance Measurement Group7
Measurement Method
Sending probes with increasing rate
(like pathChirp)
Measuring the one-way delay :as we reach the free capacity of a link the OWD increases sharply
CNL - Network Performance Measurement Group8
Measurement Method
Instead of measuring OWD we will measure the ratio of inter arrival time and the inter probe spacing (t*/t)to avoid problem comes from the unsynchronized clocks of the sender and receiver
tt, as LPR (we are below the AB) t*/t linear , as LPR available bandwidth (we above the AB)
CNL - Network Performance Measurement Group9
Measurement Method
t*/t is sensitive for the mean of the free capacity along a route, and also for the coefficient of variation () of the CT
CNL - Network Performance Measurement Group10
difficulties in real measurements:• fluctuations in the measured data (even in stationary CT)
averaging over some chirps• small number of probes not to cause serious congestion• sparsely spaced probes to cover the whole regions of the possible free capacity • sparsely spaced probes we need a function to fill out the space between two measured points
Measurement Method
CNL - Network Performance Measurement Group11
• f x, as probing rate x
• smooth and monotone increasing
• asymptotically linear for large x f xx
The function we are looking for:
The function has at least 3 parameters:
• two to fit the asymptotic slopes
• one to allow for the Cross Traffic dependent speed of transition
Analytic Approximation
CNL - Network Performance Measurement Group12
Analytic Approximation
The function is:
We can determine the parameters of best fit using the Levenberg-Marquardt Algorithm.
CNL - Network Performance Measurement Group13
Analytic Approximation
The fits were generally good both for Poisson and Weibullian-renweal cross traffic
(with different mean and coefficient of variation ())
CNL - Network Performance Measurement Group14
Estimation of Available Bandwidth
thxwhere f xintcloga)
Two algorithms to select the transition scale:
• threshold based: thxf xs (we used s
• intersection based (the intersection of the two asymptotes): int
CNL - Network Performance Measurement Group15
Comparing the performance of thandint
th: sensitive to mean,
but worsen as burstiness increases
int: also sensitive to burstiness,
Estimation of Available Bandwidth
CNL - Network Performance Measurement Group16
Laboratory Experiments
Validation: compare with the standard pathChirp toolin controlled environment
Network testbed:
Probe stream
Controlled CT
- Receiver tool - DAG monitor
- CT generator
- Sender tool
CNL - Network Performance Measurement Group17
Laboratory Experiments
estimations by pathChirp, and by the combinations of the intersection and threshold methods
CNL - Network Performance Measurement Group18
Conclusions and Future plans
• we have developed an improved method for available bandwidth estimation, resulting better estimations• first steps to work out the underlying theoretical model for evaluation of the measured data
In the future:• develop a complete measurement package• explore different strategies for sampling the investigated curve• find more robust alternative transition scale selection algorithms
CNL - Network Performance Measurement Group19
Thank you for your attention!